Capacitively Coupled Electrocardiogram Measuring System and Noise Reduction by Singular Spectrum Analysis

A wearable electrocardiogram (ECG) measuring system is designed based upon capacitively coupled biopotential sensing electrodes. The sensing electrodes are made from the standard printed-circuit board. Using a reversely connected diode to provide the required high-value bias resistance, the pickup circuit for biopotential sensing is implemented by a high-input-impedance instrumentation amplifier. Two different configurations of the ECG measuring system are constructed and experimentally tested. One is a floating ground configuration in which only two sensing electrodes are used for ECG signal acquisition. Another is the passive ground configuration in which an additional grounding electrode is employed as the reference for common-mode noise suppression. The ECG signal can be obtained through thin clothes for both cases but performs lower signal-to-noise ratio. In order to improve the quality of the obtained signal, an algorithm based on a singular spectrum analysis is designed for noise reduction. A matching template is introduced to pick out the critical principal components automatically. Experimental results show that, with the aid of the proposed algorithm, satisfied ECG and respiration signals can be effectively obtained outside cotton-fiber clothing.